Pneumatic impact breakers of the above type provide an effective breaking by a high impact energy but generate at the same time external vibrations and internal blows which have a detrimental influence on the operator as well as on the mechanical parts. Detrimental blows or so called bottom blows of the hammer piston occur as the application or feeding force on the breaker is very low, nill or negative. A negative feeding force is accomplished as the breaker is lifted up, for instance when the working implement has become jammed.
In previous impact breakers of the above type, these bottom blows have been difficult to dampen out fully, and, in order to make the parts withstand the stress forces and to ensure a safe assemblage of the breaker, the parts thereof, including the housing itself, have to be oversized. It has also been necessary to use extra strong tie bolts and/or threaded joints to keep the parts safely together. An example thereon is shown in U.S. Pat. No. 3,179,185, FIG. 4, in which the damping means for absorbing the hammer piston energy at bottom strokes comprises an annular elastomer element. In practice, this known arrangement has no ability to absorb the kinetic energy of the hammer piston, and moreover, the service life of this impact damping elastomer element will be very short.
Another example is shown in U.S. Pat. No. 3,451,492. The impact breaker illustrated therein comprises a hammer piston which has a comparatively long impact delivering stem portion in relation to the length of the piston head. This means that, due to the inevitable tilting of the piston occurring when the stem portion is out of guiding engagement with the forward small diameter cylinder bore extension, there must be provided a relatively large play between the stem portion and the bore to avoid too a violent metallic contact therebetween. This results in a relatively wide leak gap around the stem portion, and, accordingly, a rather ineffective damping volume entrapped between the hammer piston, the cylinder bore and the forward shoulder in the cylinder bore. Despite a rather large play between the piston stem and the cylinder bore extension and a following poor air volume energy absorption, there is an undesirably severe wear of the piston stem and the cylinder bore extension due to metallic contact therebetween.